The invention involves a caliper for disk brakes according to the preamble of claim 1.
Higher and higher demands are being placed on the performance of modern disk brakes. Thus the brake itself and especially the caliper housing should be light on the one hand, in order to minimize the unsprung weight on the vehicle wheel while on the other hand, the caliper must be very rigid so that it does not bend very much under large stress.
The use of aluminum alloys for the brake caliper, instead of the conventional iron workpieces, is increasing in order to save weight. Aluminum alloys have the disadvantage, however, that their strength decreases for temperatures above 300.degree. C. Such temperatures can certainly occur for disk brakes in extreme cases. To solve this problem materials are suitable which are known as metal-matrix composite materials. These involve composite materials made of metal and ceramic particles or fibers of varying lengths. In order to cast brake calipers, a composite material of aluminum and ceramic particles is especially suitable, for example particles of silicon carbide.
Such a metal-matrix composite material with ceramic particles is considerably less flexible than aluminum alloys. It allows the construction of lightweight brakes which are considerably reduced in construction space as opposed to brakes made of aluminum and nevertheless have a high rigidity. A disadvantage of this composite material is its high hardness which is attributable to the ceramic particles. A rough-cast caliper housing is thus very difficult to subsequently machine, in order, for example, to put in threading for the hydraulic fluid supply connection or a gasket ring groove in the brake cylinder. The processing is laborious, expensive and only possible using diamond tools, unless one is willing to put up with minimal service life for the tools. Subsequent machining is thus out of the question for economic reasons.
For the casting of metal-matrix composite materials, the known "lost-foam-process" is available. In this process, a high-resistance foam core of the caliper housing is manufactured which is embedded in a casting mold in sand and then cast using the metal-matrix composite material. It is possible to cast undercuts using this process so that the unfinished part does not have to be subsequently machined, at least as far as the undercuts are concerned. In this process, several subsequent machining steps are already saved. At other positions, a subsequent machining is necessary in spite of this, especially if very small tolerances are necessary, which cannot be achieved in the mold. This is regularly the case for threaded connections, piston bore holes, grooves or recesses.